1. Field of the Invention
The present invention relates to a camera system having the so-called diaphragm or shutter making use of the property of photoelectric or photomagnetic elements whose light permeability is varied in accordance with the applied electric or magnetic field, particularly a camera system in case the interchangeable lens for a camera is provided with the diaphragm or shutter making use of the property of matter.
2. Description of the Prior Art
Until now, the mechanical diaphragm device is mainly applied as diaphragm device for camera, the mechanical diaphragm device needs corresponding mechanism for operating the device. Thus, in case of a camera with the interchangeable lens it is necessary to provide a complicated mechanism for connecting the diaphragm device at the side of the interchangeable lens to the camera body, which causes the increase of the manufacturing cost, the size and the restriction of the freedom of the design of the camera.
The above-mentioned difficulties taken into consideration, various kinds of diaphragm device making use of the property of matter, namely the photoelectric and the photomagnetic element whose light permeability is varied in accordance with the applied electric or magnetic field have been proposed. As the above-mentioned photoelectric or photomagnetic element, the Kerr cell transparent ferroelectric substance (PLZT) having the double refraction, the liquid crystal and the Faraday element can be pointed out, whereby they are applied in combination with the polarizer and the analyzer. Apart from the above, the electrochromie element and the element having the electrophoresis are also known.
These diaphragm devices making use of the property of matter enjoy many features which the conventional mechanical diaphragm devices do not have. Namely, the diaphragm device making use of the property of matter do not need any connecting mechanism so that they are compact and light. The freedom of the camera design is largely increased. Further, quite free from the shock at the start of the diaphragm operation and the noise connected therewith, no undesirable feeling is given to the photographer. Further, the diaphragm closing confirmation operation can easily be made by means of only one switch. Further, the diaphragm making use of the property of matter can be operated at least by means of the electric circuit means, it can easily be adopted to the recent electronic camera, whereby there is much possibility for the diaphragm to make a large step toward the realization of the totally electronic camera in the future, which is quite profitable. It goes without saying that the conventional mechanical shutter can be replaced with the shutter making use of the property of matter in the same way as the diaphragm making use of the property of matter, which is also profitable.
Hereby, two kinds of the diaphragm making use of the property of matter can be thought out. The one is the light permeability control system in accordance to which the intensity of the electric or the magnetic field to be applied is controlled so as to control the light permeability in an analogue way, while the other is the area control system in accordance to which a plural number of the electrodes are arranged in the diaphragm device making use of the property of matter so as to vary the area in the light permeable state.
Further, in case of the former light permeability control system the delicate control is difficult in case the applied voltage--light permeability characteristics of the element is sharp, whereby further the applied voltage--light permeability characteristics itself has a temperature characteristics, which needs a temperature compensation so that the driving circuit is expensive.
Further, in case of this system it is necessary to apply voltage evenly to the whole element, so that the distance between the base plates between which the element is to be sandwiched has to be strictly constant, which gives much difficulty to the manufacture of cell.
Consequently, the latter area control system is much realizable. However, this system has also the following shortcoming.
The diaphragm making use of the property of matter of the area control system is driven by means of the digital signal, whereby in case the diaphragm making use of the property of matter is arranged in the interchangeable lens for camera, while the driving circuit is arranged at the side of the camera body, it is necessary to provide at least the same number of the contacts as that of the electrodes at the side of the camera body and the interchangeable lens.
Now, let the number of steps of the diaphragm making use of the property of matter be 7, each step having between steps of 1/3. Hereby, at least 21 (=3.times.7) electrodes is necessary, in case nothing is devised out. Thus, the same number of contacts as that of the electrodes are necessary, whereby it is almost impossible to provide such a large number of contacts at the lens mount.